1. Field of the Invention
The present invention relates to a rubber composition suitable for use as a tire and, more particularly, to a rubber tire composition having improved abrasion resistance, and being especially suitable for use as a truck tire or a bus tire.
2. Description of the Background Art
Heretofore, the use of ISAF-grade carbon black as a highly reinforcing packing for rubber has been well known. Recently, however, there has been a great demand for carbon black which is capable of improving abrasion resistance of a tire, especially a pneumatic tire which experiences heavy loading, due to improved durability of a tire carcass and the desire to conserve natural resources.
The grade of carbon black which is used as a reinforcing agent of a rubber composition for a tire tread used for heavy loading has been changed from ISAF-grade to SAF-grade. This is because SAF-grade carbon black particles are finer than those of ISAF-grade. In general, when carbon black is compounded into rubber to improve abrasion resistance, it is desirable to use a finely divided carbon black. However, even if the carbon black particles are finer than SAF-grade particles, abrasion resistance is not necessarily improved since the dispersibility of the carbon black in the compounded rubber is remarkably lowered.
In order to improve abrasion resistance, various investigations have been conducted focusing on the colloidal characteristics of carbon black. Japanese Patent Application Laid-Open No. Sho 62-290738, for example, discloses a method for improving abrasion resistance by controlling, aggregate distribution of carbon black. However, even this method does not achieve satisfactory abrasion resistance to a level demanded at the present time.
In addition, by narrowing the aggregate distribution, abrasion resistance is not remarkably improved and reaches a limit.